Re[2]: LLD Question for Gross Alpha/Beta Counting

[roseb@SMTP-gw.gdls.com (Boyd H Rose)]

I do not have a reference available which tells how to address your specific 
counting question.  Also, without knowing more about your source sample 
characteristics (nuclide(s), substrate(s), etc.) and counting parameters, my 
response will be very general.

With your type of detector configuration, you are able to set your detector 
voltage such that you can count either alpha or alpha+beta.

You could determine LLD for gross alpha/beta counting by calculating the alpha 
and beta LLDs separately and then adding them or you could determine LLD from 
the alpha+beta proportional region plateau.  Your LLDs as determined by both 
methods may and most likely will differ due to various factors (counts taken at 
different times as opposed to coincidentally, etc.).  As the number of counts 
increase (sample size becomes large or more samples are taken) for a given 
source sample, the LLD's as determined by the two methods should converge.

To determine LLD by adding the separate alpha and beta LLD's, you can refer many
standard statistics references on performing operations (summing, multiplying, 
etc.) on statistical measurements.  Radiation Detection and Measurement by Knoll
gives a good summary of how such an addition is done for counting measurements.

Also, you may want to review NCRP Report No. 58, A Handbook of Radioactivity 
Measurements, or more current reference for proportional counting procedures.  
There are also two recent articles in Health Physics (Feb, Mar, or Apr. 1997) by
Fong, S.H., et. al. on LLD.

I hope this is some assistance to you.

Boyd H. Rose, CM
Radiation Protection Officer
General Dynamics Land Systems Division
roseb@gdls.com

The opinions expresses above are solely my own and do not under any circumstance
 reflect those of my employer.

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At 02:01 PM 6/25/97 -0500, Jason Armstrong wrote: 

>A sealed proportional counter. 

At 02:01 PM 6/25/97 -0500, you wrote: >Jason Armstrong wrote:
>
>>When determining the LLD for Gross alpha/beta counting, do you calculate the 
>LLD for alpha and the LLD for beta then add the two together for a gross 
>alpha/beta LLD?
>     
>>I tried looking for a reference for doing this, but to no avail. 
>     
>>Thanks in advance for your help,
>
>What is your detection system configuration?  GM and scaler / rate meter?  
>Proportional counter? Phoswich?
>
>Boyd H. Rose, CM
>Radiation Protection Officer
>General Dynamics Land Systems Division 
>roseb@gdls.com
>
>The opinions expresses above are solely my own and do not under any 
circumstance
>reflect those of my employer.
>
>